Master disk having grooves of different depths for magnetic printing and manufacturing method therefor
A master disk has an aspect ratio of a width of a groove to a depth thereof to facilitate embedding of a soft magnetic film in the groove for stabilizing magnetic printability. The master disk has at least two differently shaped grooves, in each of which the width of the groove is equal to the width in the sector direction of a servo pattern and the depth is varied. A servo pattern has a width equal to a width of the groove in the sector direction, with the depth of the groove being proportional to the servo pattern width. At least two depths of grooves are provided for embedding magnetic materials on a substrate of the master disk. The depth of the groove for embedding the soft magnetic film is made shallow in a region where the pattern width of the servo pattern is narrow and made deep in a region where the pattern width is wide.
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The invention relates to a master disk for magnetic printing and a method of manufacturing the same. More particular, the invention is directed to a master disk and its method of manufacturing for magnetic printing, provided so as to write servo signals for positioning a head or specified data onto a surface of a magnetic disk using magnetic printing technology. The head carries out writing of data to/reading of written data from the surface of the magnetic recording disk in a hard disk drive (hereinafter referred to as an “HDD”), which drive is currently mainstream as external computer storage. The magnetic recording disk has as a recording material at its surface a magnetic film.
In the above-described HDD, recording and reproducing of data are carried out while a magnetic head floats on a surface of a rotating magnetic disk as a magnetic recording medium, kept there several tens nanometers from the surface of the disk by a floating mechanism known as a slider. On the magnetic recording medium, bit information is stored in data tracks arranged in concentric circles on the magnetic recording medium. The data recording/reproducing head is moved and positioned at a high speed onto a target data track on the magnetic recording medium to record and reproduce the data.
On the surface of the magnetic recording medium, positioning signals (servo signals) for detecting a position of the head relative to the data track, are written in concentric circles. This allows the head carrying out the recordation and reproduction of data to detect its own position at fixed time intervals. The servo signal is written by using a specialized device known as a servo writer after the magnetic recording medium is mounted in an HDD device, so that the center of the written servo signal causes no eccentricity to the center of the magnetic recording medium (or the center of the path (orbit) of the head).
A recording density in a present stage of development has reached up to 100 Gbits/in2 and, along with this, the recording density is increasing at an annual rate of 60%. Accompanying this, the density of the servo signal used by the head for detecting its own position is increasing, and the time for writing the servo signal has also tended to increase year by year. An accompanying increase in the writing time of the servo signal has become one of the major causes of reduction in manufacturing productivity and an increase in the cost of the HDDs.
Recently, in contrast with the above-described method of writing the servo signal using a writing head of the servo writer, a technological development has occurred concerning a method for dramatically reducing the writing time of servo information. This involves writing the servo signal in a lump by magnetic printing.
The initial demagnetization step shown in
Moreover,
As shown in
First step: On the surface of a silicon substrate 51 (with a substrate thickness of about 500 μm), a resist 52 (with a thickness of 1.2 μm) is applied by using a spin coater (
Second step: By employing a reactive plasma-etching method (reaction gas: methane trichloride), the silicon substrate 51 is subjected to dry etching to the depth of 500 nm (
Third step: By employing a sputtering method, deposition of a soft magnetic film 53 of Co (cobalt) is carried out to a thickness of 500 nm (
Fourth step: After the deposition of the Co soft magnetic film 53, the silicon substrate 51 is immersed in a solvent that dissolves the resist 52 (while employing ultra sound and the like as necessary), by which the resist 52 between the Co soft magnetic film 53 and the silicon substrate 51 is dissolved to remove it (
Japanese Official Gazettes disclosing prior art relating to the invention are described as follows.
The art described in a Japanese patent publication No. JP-A-2001-34938, relates to a master information carrier, by which high density information signals can be uniformly and stably recorded over the whole face of a magnetic recording medium, and a method of manufacturing the carrier. The carrier is provided with a substrate and a ferromagnetic thin film disposed on the substrate so as to form a pattern arranged to correspond to a magnetic pattern with the surface of the ferromagnetic film made approximately flat. Moreover, the art described in a PCT patent publication, WO 00/26904 relates to a master information carrier and a magnetic recording method that uses the carrier, in which a figure pattern corresponding to an arrangement of information signals for being recorded in a magnetic recording medium is provided by an arrangement of ferromagnetic thin films deposited on the surface of a non-magnetic substrate.
Line widths of the patterns range from one to several lines. In order to carry out magnetic printing of the servo patterns, the same patterns as the servo patterns must be formed on a master disk as patterns of soft magnetic film. The thickness of the soft magnetic film is very important. An excessively thin film thickness causes magnetic saturation when a magnetic field to be printed is applied, which results in leakage of a magnetic flux to the magnetic recording media facing the soft magnetic film. This, in the worst case, causes inversion in magnetization to produce a problem that a region where the data should be “0” have data of “1”.
Namely,
-
- Pattern width: 0.7 μm→
- Thickness of the soft magnetic film: 0.20 μm or more
- Pattern width: 0.35 μm→
- Thickness of the soft magnetic film: 0.20 μm or more
- Pattern width: 0.2 μm→
- Thickness of the soft magnetic film: 0.075 μm or more
- Pattern width: 0.1 μm→
- Thickness of the soft magnetic film: 0.050 μm or more
- Pattern width: 0.7 μm→
When the pattern width of the servo pattern is from 0.1 to 0.7 μm, the thickness of the soft magnetic film must be 0.20 μm or more to avoid magnetic saturation in all of the regions. Practically, however, within film nonuniformity arising in a photo-process and deposition of the soft magnetic film must be taken into consideration. Therefore, the thickness of the soft magnetic film should be 0.30 μm or more. Different cross-sectional shapes, in which a Co soft magnetic film is embedded in a groove etched in a photo-process, are shown respectively in
From
The invention was made in view of such a problem, with an object to provide a master disk for magnetic printing that enables control of an aspect ratio of a width of a groove to a depth thereof, and along with this, facilitates embedding of a soft magnetic film in the groove for stabilizing magnetic printability by the master disk. Another object is to provide a method of manufacturing such a master disk.
In order to accomplish these objects, the invention provides in a master disk for forming a magnetic pattern in a magnetic recording medium by magnetic printing, at least two or more kinds of depths of grooves for embedding magnetic materials on a substrate of the master disk. In accordance with the other aspects of the invention the depth of the groove for embedding the magnetic material is proportional to a pattern width in a sector direction of a servo pattern. Thus, the depth of the groove for embedding the magnetic material is made shallow in a region where the pattern width of the servo pattern is narrow and made deep in a region where the pattern width is wide. The depth of the groove for embedding the magnetic material may vary stepwise with respect to the pattern width. In a method of manufacturing such a master disk for magnetic printing, the groove for embedding the magnetic material is formed by photolithography in a repetitive manner.
With respect to the above-described subject, the problem caused at the deposition can be eliminated by taking measures that vary the depth of the groove for embedding the soft magnetic film in the silicon substrate of the master disk, depending on the pattern width of the soft magnetic film in the sector direction. The groove depth need not be varied in an analog manner, but may be varied stepwise. When classification of the depths of the grooves is determined, for example, with the magnetic field strengths shown in
As described above, characteristic of the invention is that the groove width is constant in the sector direction of the servo pattern, whereas the depth is varied. The servo pattern width “a” in
The depths are required to be such that the soft magnetic films have thicknesses whereby no magnetic saturation occurs due to printing magnetic fields therein. According to the results of analyses of magnetic field strengths on the surface of the magnetic recording medium as shown in
-
- Pattern width: 0.35 μm to 0.7 μm→
- Thickness of the soft magnetic film: 0.20 μm
- Pattern width: 0.1 μm to 0.2 μm→
- Thickness of the soft magnetic film: 0.075 μm
- Pattern width: 0.35 μm to 0.7 μm→
The analyses of the magnetic field at the surface of the magnetic recording medium shown in
A plurality of photomasks becomes necessary. The number of such photomasks corresponds in number to the possible number of different film thicknesses of the soft magnetic films (the possible number of the depths of the grooves). Namely, in the example, the required number of thicknesses (depths) is two, so that a photomask exclusively for a region with a film thickness of 075 μm and a photomask exclusively for a region with a film thickness of 0.20 μm, are required. In the following, explanations are provided for the successive process steps.
First step: A silicon substrate 21 (substrate thickness of about 500 μm) is prepared (FIG, 2(a)).
Second step: A resist 22 is applied (
Third step: Patterning is carried out using a photomask for application only for a region with a soft magnetic film having a thickness of 0.075 μm (
Moreover, in an unillustrated development step, parts of the resist irradiated with light are removed to print the pattern of the photomask on the resist.
Fourth step: By employing a reactive plasma-etching method (reaction gas: methane trichloride), dry etching of the silicon substrate 21 is carried out to a depth of 75 nm to form grooves (
Fifth step: The resist 22 is removed by a resist stripper to expose the face of the silicon substrate 21 (
Sixth step: A resist is applied again (
Seventh step: Patterning is carried out using a photomask for application only to a region with soft magnetic film having a thickness of 0.2 μm (
Moreover, in the unillustrated development step, parts of the resist irradiated with light are removed to print the pattern of the photomask on the resist.
Eighth step: By employing a reactive plasma-etching method (reaction gas: methane trichloride), dry etching of the silicon substrate 21 is carried out to a depth of 200 nm to form grooves (
Ninth step: The resist 22 applied in the sixth step is removed by a resist stripper to expose the face of the silicon substrate 21 (
Tenth step: A soft magnetic film 23 is deposited on the silicon substrate 21 by a sputtering device and the like. At this time, the soft magnetic film is made to have a thickness from the bottom of the grooves measured such that the film extends sufficiently above the surface of the silicon substrate 21 (
Eleventh step: The portion of the soft magnetic film 23 deposited above the surface of the silicon substrate 21 is removed by CMP (Chemical Mechanical Polishing) (
In the above-explained eleventh step, by knowing beforehand the proper rate of polishing the silicon (Si) substrate and the polishing rate of the magnetic film of Co and the like by CMP, and also knowing the thickness of the soft magnetic film deposited on the silicon substrate, it becomes possible to estimate the polishing time with CMP. Actually, however, the polishing is carried out with some margin given to the estimated polishing time. At the early stage of the polishing, the soft magnetic film deposited on the silicon substrate is polished. When the polishing reaches the silicon substrate, the speed of the polishing is slowed to allow only a small amount to be polished in a unit time.
In the invention, the resist is used as an etching mask. However, alternatively a SiO2 film can be used as an etching mask. This, however, requires complicated processes to be performed as described below, in which the previously-described first step to the fourth step and the fifth step to the eighth step are replaced by the respective steps described below. Characteristic of using a SiO2 mask is that polishing selectivity of Co to SiO2 film is increased at the eleventh step, and the SiO2 film is slow to be polished, which provides an advantage in that the depth of the groove embedding the soft magnetic film is provided accurately.
When a SiO2 film is used as an etching mask, the first step and fifth step each include a thermal oxidation treatment of the silicon substrate to form the SiO2 film on the silicon surface. In each of the second step and sixth step of the process a resist is applied to the face of the SiO2 film. In both the third step and the seventh step, patterning of the resist is carried out for development. In each of the fourth step and eight step the following is performed. The SiO2 film is etched using the mask of the resist. Next, ashing of the resist is carried out. Then etching of the silicon substrate is carried out using the SiO2 film mask.
As was explained above, according to the invention, in a master disk for forming a magnetic pattern in a magnetic recording medium by magnetic printing, at least two different depths of grooves for embedding magnetic materials are provided on a substrate of the master disk. Therefore, the depths of the grooves for embedding the soft magnetic film can be made shallow in a region where the pattern width of the servo pattern is narrow and made deep in a region where the pattern width is wide. This enables control of an aspect ratio of width to depth to facilitate embedding the soft magnetic film in the groove. This can provide stabilization of magnetic printability by the master disk.
Claims
1. A master disk for magnetic printing, the master disk forming a magnetic pattern in a magnetic recording medium by the magnetic printing, the magnetic disk including
- a substrate having grooves, the grooves including grooves of different depths; and
- magnetic materials embedded on a substrate in the grooves of different depths.
2. A method of manufacturing the master disk of claim 1, including forming the groove by repetitive photolithography.
3. The master disk for magnetic printing as claimed in claim 1, wherein the depths of the grooves for embedding the magnetic material is proportional to a pattern width in a sector direction of a servo pattern.
4. The master disk for magnetic printing as claimed in claim 3, wherein the depth of the grooves for embedding the magnetic material varies stepwise with respect to the pattern width of the servo pattern.
5. A method of manufacturing the master disk of claim 3, including forming the grooves by repetitive photolithography.
6. A method of manufacturing the master disk of claim 4, including forming the grooves by repetitive photolithography.
7. The master disk for magnetic printing as claimed in claim 3, wherein the grooves for embedding the magnetic material have a first region where the pattern width of the servo pattern is narrow and a second region where the pattern width is wide, wherein the grooves are shallow in the first region, and deep in the second region.
8. The master disk for magnetic printing as claimed in claim 7, wherein the depth of the grooves for embedding the magnetic material varies stepwise with respect to the pattern width of the servo pattern.
9. A method of manufacturing the master disk of claim 8, including forming the grooves by repetitive photolithography.
10. A method of manufacturing the master disk of claim 7, including forming the grooves by repetitive photolithography.
4723903 | February 9, 1988 | Okazaki et al. |
6748865 | June 15, 2004 | Sakurai et al. |
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07-153122 | June 1995 | JP |
2001-034938 | February 2001 | JP |
WO00/26904 | May 2000 | WO |
Type: Grant
Filed: Mar 1, 2004
Date of Patent: Jan 30, 2007
Patent Publication Number: 20040228035
Assignee: Fuji Electric Holdings Co., Ltd. (Tokyo)
Inventor: Hiroyuki Yoshimura (Nagano)
Primary Examiner: A. J. Heinz
Attorney: Rabin & Berdo, P.C.
Application Number: 10/788,424
International Classification: G11B 5/86 (20060101); G11B 5/82 (20060101);